But Simon Porter at the Southwest Research Institute in Boulder, Colorado, and colleagues have calculated that because Pluto loses between 1027 and 1028 nitrogen molecules a second, it should have lost between 0.3 and 3 kilometres of ice over 3.5 billion years, erasing much of the small crater record (Icarus, doi.org/zx4).

There’s hope, though&colon; Pluto’s ices also contain methane, which preserves craters better than nitrogen. In addition, Pluto’s largest moon Charon is covered with hard water ice, and so should preserve a pristine impact record.

This article appeared in print under the headline “Pluto’s pockmarks evaporate quickly”